1. Field of the Invention
The present invention relates to methods of producing ceramic slurry, a ceramic slurry composition and a ceramic green sheet used for manufacturing a multilayer ceramic electronic part, and a method of producing a multilayer ceramic electronic part. Particularly, the present invention relates to methods of producing ceramic slurry and a ceramic slurry composition used for manufacturing a multilayer ceramic electronic part such as a monolithic ceramic capacitor, a ceramic multilayered substrate, etc., and methods of producing a ceramic green sheet and a multilayer ceramic electronic part using the ceramic slurry or the ceramic slurry composition.
2. Description of the Related Art
A multilayer ceramic electronic part such as a monolithic ceramic capacitor, a ceramic multilayered substrate, or the like is usually manufactured through the steps of laminating ceramic green sheets, compressing the laminated ceramic green sheets, and then heat-treating the laminated product to sinter ceramic and electrodes.
For example, in manufacturing a monolithic ceramic capacitor having a structure in which internal electrodes 2 are provided in a ceramic element 1, and a pair of external electrodes 3a and 3b are provided to be connected to the internal electrodes 2 which alternately lead to the different side ends, as shown in FIG. 1, the following method is used.
(1) First, a capacity forming internal electrode is provided on a ceramic green sheet to form a sheet 11 provided with an electrode (FIG. 2).
(2) Next, a predetermined number of the sheets 11 provided with electrodes are laminated, and ceramic green sheets (outer layer sheets) 21 without electrodes are laminated on the upper and lower sides of the laminated sheets, followed by compression to form a laminated product (laminated compressed body) in which the ends of the internal electrodes 2 are alternately end at the different side ends.
(3) The laminated compressed body is burned under predetermined conditions to sinter the ceramic, and then conductive paste is coated at both ends of the laminated product (ceramic element) 1 (FIG. 1) after burning, and baked to form the external electrodes 3a and 3b (FIG. 1) connected to the internal electrodes 2. As a result, the monolithic ceramic capacitor shown in FIG. 1 is obtained.
Other multilayer ceramic electronic parts such as a laminated ceramic multilayered substrate, etc. are also manufactured through the step of laminating ceramic green sheets.
Each of the ceramic green sheets used for manufacturing the multilayer ceramic electronic parts is generally produced by a method in which a ceramic powder is mixed with a dispersion medium (solvent), a dispersant, a binder, a plasticizer, etc., at a predetermined ratio, and disintegrated by using a medium-type dispersing machine such as a bead mill, a ball mill, an attritor, a paint shaker, a sand mill or the like, to produce ceramic slurry and the thus-produced ceramic slurry is formed in a sheet having a predetermined thickness by the doctor blade method, and then dried.
In recent years, various multilayer ceramic electronic parts such as a monolithic ceramic capacitor, like other electronic devices, have been required to have a smaller size and higher performance. Therefore, the ceramic green sheets used for manufacturing the multilayer ceramic electronic part are required to have a small thickness, thereby causing the need to use very thin ceramic green sheets having a thickness of 10 xcexcm or less.
In order to product such a thin ceramic green sheet, a ceramic slurry comprising a ceramic raw material sufficiently dispersed therein must be used for producing the ceramic green sheets, and thus a ceramic raw material comprising a fine powder having an average particle diameter of about 0.01 to 1.0 xcexcm must be used as a ceramic raw material powder.
However, the conventional method of producing ceramic slurry comprising mixing the ceramic powder with a dispersion medium (solvent), a dispersant, a binder, a plasticizer, etc., at a predetermined ratio and then disintegrating the mixture by using a medium-type dispersing machine such as a bead mill, a ball mill, an attritor, a paint shaker, a sand mill or the like, makes it difficult to sufficiently disperse the ceramic fine powder of about 1.0 xcexcm or less. Under actual conditions, therefore, ceramic slurry having dispersion uniformity cannot be obtained, thereby causing difficulties in producing a high-quality thin ceramic green sheet.
Namely, the ceramic green sheet produced by using the ceramic slurry produced by the above-described conventional method has problems in that (1) the surface smoothness is insufficient, (2) a high density and sufficient tensile strength cannot be obtained, and (3) the rate of shrinkage varies with positions in the burning step after lamination due to nonuniform distribution of resins such as the binder, the plasticizer, etc., to fail to obtain sufficient dimensional precision. Particularly, these problems become significant when using a binder having a high degree of polymerization.
In some cases, the conventional method of producing a ceramic slurry comprises dispersing the ceramic powder by forcedly applying collision or impact using a ball mill filled with balls, or a bead mill filled with beads in order to improve dispersibility. In this case, there is a problem in that the ceramic powder is greatly damaged due to the excessive disintegration force of collision or impact to cause deterioration in crystallinity of the ceramic powder and an increase in the specific surface area, thereby failing to obtain a multilayer ceramic electronic part having desired electric properties.
In some cases, a high-pressure dispersion method is used in which slurry containing a ceramic powder is caused to flow under high pressure so that the ceramic powder is dispersed by collision or impact force. However, in this method, the high-pressure disintegration force alone is lower than the method of disintegrating by forced collision or impact using the medium-type dispersing machine such as a ball mill, a bead mill, or the like, causing difficulties in sufficiently disintegrating strongly agglomerated particles. There is thus a problem in that since sufficiently dispersed ceramic slurry cannot be produced, and a high-quality ceramic green sheet cannot be obtained.
Another dispersion method comprises causing a slurry containing a ceramic powder and discharged from a small orifice or nozzle by applying high pressure thereto to collide with a solid wall of a hard material, for example, such as cemented carbide, ceramic, diamond, or the like, or causing the materials discharged from a plurality of small orifices or nozzles to collide with each other. In this method, when the same energy as the above high-pressure dispersion system is applied to the slurry, the stress loaded on the flowing ceramic powder can be increased. However, even when strongly agglomerated particles can be disintegrated, a sufficiently dispersed ceramic slurry cannot be produced because of poor uniformity, thereby causing the problem of failing to obtain a high-quality ceramic green sheet.
Furthermore, defects such as pinholes readily occur in the thin ceramic green sheet, and the use of such ceramic green sheets for manufacturing the monolithic ceramic capacitor shown in FIG. 1 causes a short circuit (short circuit failure) between the internal electrodes 2 opposed to each other with the ceramic layer formed therebetween.
The defects of the ceramic green sheet which cause such a short circuit failure, are mainly produced due to the presence of the undissolved binder in the ceramic slurry used for producing the ceramic green sheet. The content of the undissolved binder is found to greatly influence the rate of occurrence of the short circuit failure.
As the binder used for the ceramic slurry used for producing the ceramic green sheet, a polyvinyl butyral resin, a cellulose resin, an acrylic resin, a vinyl acetate resin, a polyvinyl alcohol resin or the like, is generally used. In general, a binder solution is used, which is prepared by mixing and stirring such a binder and a solvent such as toluene, xylene, ethyl alcohol, isopropyl alcohol, butyl alcohol, or the like.
However, the binder cannot be completely dissolved in the solvent only by mixing and stirring the binder and the solvent, and thus undissolved material remains in the binder solution. Although a possible method of separating and removing the undissolved material is filtration, the binder solution has high viscosity and thus high resistance in filtration, thereby limiting use of a filter having a small pore size. Under actual conditions, it is difficult to completely remove the undissolved material.
Another possible method comprises filtering the ceramic slurry after the binder containing the undissolved material is added. However, this method is limited because a filter having a small pore size is easily clogged with the ceramic powder.
The present invention has been achieved in consideration of the above situation, and an object of the present invention is to provide methods of producing ceramic slurry and a ceramic slurry composition from which an undissolved binder is precisely removed, and methods of producing a ceramic green sheet and a multilayer ceramic electronic part using the ceramic slurry or ceramic slurry composition.
In order to achieve the object of the present invention, a method of producing ceramic slurry used for producing a ceramic electronic part comprises the mixing disintegration step of mixing a ceramic powder having an average particle diameter of about 0.01 to 1 xcexcm with a dispersion solvent and disintegrating the ceramic powder by a medium-type dispersion method using a dispersion medium such as balls, beads, or the like to obtain mixed and disintegrated slurry, and the high-pressure dispersion step of dispersing the mixed and disintegrated slurry under a high pressure of about 100 kg/cm2 or more to obtain disperse slurry. The ceramic powder having an average particle diameter of about 0.01 to 1 xcexcm is mixed with the dispersion solvent, and disintegrated by the medium-type dispersion method using the dispersion medium such as balls, beads, or the like to obtain the mixed and disintegrated slurry, and the mixed and disintegrated slurry is dispersed under a high pressure of about 100 kg/cm2 or more to obtain disperse slurry in which the ceramic powder is sufficiently dispersed. Namely, the ceramic powder is dispersed by a combination of the medium-type dispersion method and the high-pressure dispersion method so that the ceramic powder can be uniformly dispersed while suppressing deterioration in crystallinity of the ceramic powder and an excessive increase in the specific surface area, thereby producing high-quality ceramic slurry.
In the present invention, as the dispersion solvent, a solvent containing a dispersant, a plasticizer, and an antistatic agent can be used, and other additives may be added to the solvent.
In the present invention, the high-pressure dispersion means is a wide concept which means the method of dispersing slurry by using a high-pressure dispersing apparatus in which a solution to be dispersed under high pressure is caused to collide with a wall or passed through a passage with a diameter gradually decreased by a taper.
Although the present invention is advantageously applied to a case in which the ceramic powder has an average particle diameter (an average primary particle diameter measured by an electron microscope) which lies in the range of about 0.01 to 1 xcexcm, the present invention can also be applied to a case in which the average particle diameter is beyond the range of about 0.01 to 1 xcexcm.
In the method of producing ceramic slurry of the present invention, mixing and disintegration may be performed by the medium-type dispersion method with a binder added.
Even when the mixing disintegration step is performed with a binder added, the ceramic powder can be uniformly dispersed without excessive damage to the ceramic powder to produce high-quality ceramic slurry.
The time of addition of the binder is not limited, and the binder may be previously mixed with the dispersion solvent or mixed at the time the ceramic powder is dispersed in the dispersion solvent.
In another aspect of the present invention, a method of producing ceramic slurry used for manufacturing a ceramic electronic part comprises the mixing disintegration step of mixing a ceramic powder having an average particle diameter of about 0.01 to 1 xcexcm with a dispersion solvent containing no binder and disintegrating the ceramic powder by a medium-type dispersion method using a dispersion medium such as balls, beads, or the like to obtain mixed and disintegrated slurry, and the high-pressure dispersion step of adding the binder to the mixed and disintegrated slurry and dispersing the resultant mixture under a high pressure of about 100 kg/cm2 or more to obtain disperse slurry.
The ceramic powder is mixed with the dispersion solvent containing no binder, and disintegrated by the medium-type dispersion method to obtain the mixed and disintegrated slurry, and the binder is added to the mixed and disintegrated slurry, followed by dispersion under a high pressure of about 100 kg/cm2 or more to obtain a slurry in which the ceramic powder is sufficiently dispersed.
Namely, the binder is partially gelled in the dispersion solvent in some cases, and thus the ceramic powder is mixed with the dispersion solvent and disintegrated by the medium-type dispersion method before the binder is added to improve the efficiency of mixing and disintegration, as compared with mixing and disintegration of the ceramic powder in a partially gelled state by the medium-type dispersion is method. Therefore, the final dispersibility of the ceramic powder can be further improved.
In still another aspect of the present invention, a method of producing ceramic slurry used for manufacturing a ceramic electronic part comprises the mixing disintegration step of mixing a ceramic powder having an average particle diameter of about 0.01 to 1 xcexcm with a dispersion solvent containing no binder and disintegrating the ceramic powder by a medium-type dispersion method using a dispersion medium such as balls, beads, or the like to obtain mixed and disintegrated slurry, the primary high-pressure dispersion step of dispersing the mixed and disintegrated slurry under a high pressure of about 100 kg/cm2 or more to obtain primary disperse slurry, and the secondary high-pressure dispersion step of adding the binder to the primary mixed and disintegrated slurry and further dispersing the resultant mixture under a high pressure of about 100 kg/cm2 or more to obtain secondary disperse slurry (final disperse slurry).
The ceramic powder is mixed with the dispersion solvent containing no binder, and disintegrated by the medium-type dispersion method to obtain the mixed and disintegrated slurry, and the mixed and disintegrated slurry is dispersed under a high pressure of about 100 kg/cm2 or more to obtain the primary disperse slurry. The binder is added to the primary disperse slurry, followed by further dispersion under a high pressure of about 100 kg/cm2 or more to obtain the secondary disperse slurry. In this case, the ceramic powder can uniformly be dispersed without excessive damage to the ceramic powder, thereby producing high-quality ceramic slurry.
In a further aspect of the present invention, a method of producing ceramic slurry used for manufacturing a ceramic electronic part comprises the primary mixing disintegration step of mixing a ceramic powder having an average particle diameter of about 0.01 to 1 xcexcm with a dispersion solvent containing no binder and disintegrating the ceramic powder by a medium-type dispersion method using a dispersion medium such as balls, beads, or the like to obtain primary mixed and disintegrated slurry, the secondary mixing disintegration step of adding the binder to the primary mixed and disintegrated slurry, and mixing and disintegrating the resultant mixture by a medium-type dispersion method using a dispersion medium such as balls, beads, or the like to obtain secondary mixed and disintegrated slurry, and the high-pressure dispersion step of dispersing the secondary mixed and disintegrated slurry under a high pressure of about 100 kg/cm2 or more to obtain disperse slurry.
The ceramic powder is mixed with the dispersion solvent containing no binder, and disintegrated by the medium-type dispersion method to obtain the primary mixed and disintegrated slurry, the binder is added the primary mixed and disintegrated slurry, and the resultant mixture is again mixed and disintegrated by the medium-type dispersion method to obtain the secondary mixed and disintegrated slurry, followed by dispersion under a high pressure of about 100 kg/cm2 or more. In this case, the ceramic powder can uniformly be dispersed without excessive damage to the ceramic powder, thereby producing high-quality ceramic slurry.
In the method of producing ceramic slurry of the present invention, a binder solution obtained by mixing and stirring a solvent and the binder, and then dispersing the binder in the solvent under a high pressure of about 100 kg/cm2 or more is used as the binder.
By using, as the binder, the binder solution obtained by mixing and stirring the solvent and the binder, and then dispersing the binder under a high pressure of about 100 kg/cm2 or more, the occurrence of gel, which is caused in direct addition of the binder, can be prevented to further improve the dispersibility of the ceramic powder.
In the method of producing ceramic slurry of the present invention, a binder solution obtained by mixing and stirring the solvent and the binder to form a binder mixed solution, and then heating the binder mixed solution under reflux at 40 to 100xc2x0 C. is used as the binder.
By using the binder solution obtained by mixing and stirring the solvent and the binder to form a binder mixed solution, and then heating the binder mixed solution under reflux at 40 to 100xc2x0 C. as the binder, the binder can be added in a state in which the binder is securely dissolved (a state without aggregation of xcexcm size), thereby further improving the dispersibility of the ceramic powder.
In the method of producing ceramic slurry of the present invention, the disperse slurry (final disperse slurry) has a viscosity of about 0.01 to 0.1 Pas. With the disperse slurry (final disperse slurry) having a viscosity of about 0.01 to 0.1 Pas, the ceramic slurry is suitable for use in the process for forming a ceramic green sheet, thereby making the present invention more effective.
In the method of producing ceramic slurry of the present invention, the medium-type dispersion method uses a ball mill or a bead mill.
By using the method using a ball mill or bead mill as the medium-type dispersion method, agglomerated ceramic particles can securely be disintegrated, making the present invention more effective.
A method of producing a green sheet of the present invention comprises forming ceramic slurry produced by the method of the present invention in a sheet on a predetermined substrate to form a ceramic green sheet having a thickness of about 0.1 to 10 xcexcm. Since the ceramic slurry produced by the above-described method comprises the ceramic powder having an average particle diameter of about 0.01 to 1 xcexcm and sufficiently dispersed in the dispersion solvent, a high-quality ceramic green sheet having a small thickness (about 0.1 to 10 xcexcm) can securely be produced by forming the ceramic slurry in a sheet. It is possible to obtain a ceramic green sheet having excellent surface smoothness, a high density, high tensile strength, and uniformity in the distribution of resins such as the binder, the plasticizer, etc., and suitable for manufacturing a multilayer ceramic electronic part.
A method of producing a multilayer ceramic electronic part of the present invention comprises forming ceramic green sheets by using ceramic slurry produced by the method of the present invention, laminating a plurality of the ceramic green sheets together with base metal internal electrodes, cutting and burning the laminated product, and then forming external electrodes.
A plurality of the ceramic green sheets formed by using the ceramic slurry produced by the method of the present invention are laminated together with base metal internal electrodes, the laminated product is cut and burned, and the external electrodes are formed thereon to obtain a high-quality multilayer ceramic electronic part having desired properties and high reliability.
In a further aspect of the present invention, a method of producing ceramic slurry comprises passing mixed slurry containing a ceramic powder having an average particle diameter of about 0.01 to 1 xcexcm and a dispersion solvent through a predetermined passage under high pressure at a flow rate which can apply a maximum shear stress of about 1000 Pa or more to the ceramic powder to disperse the ceramic powder in the mixed slurry.
Since the mixed slurry of the ceramic powder having an average particle diameter of about 0.01 to 1 xcexcm and the dispersion solvent is passed through the predetermined passage under high pressure and conditions which can apply a maximum shear stress of about 1000 Pa or more to the ceramic powder, the shear stress necessary for dispersion can be applied to the ceramic powder during the passage of the mixed slurry through the predetermined passage with less damage to the ceramic powder, thereby efficiently dispersing the ceramic powder.
In the present invention, xe2x80x9cthe mixed slurry of the ceramic powder and the dispersion solventxe2x80x9d includes a state containing the binder, the dispersant, the plasticizer, the antistatic agent, etc. Namely, the present invention also exhibits a sufficient operating effect in a case in which the mixed slurry containing additives such as the binder, the dispersant, the plasticizer, the antistatic agent, etc. is dispersed. Therefore, the method of producing ceramic slurry of the present invention includes the case in which the mixed slurry containing these additives is dispersed.
Although the present invention is advantageously applied to the ceramic powder having an average particle diameter (an average particle diameter measured by an electron microscope) in the range of about 0.01 to 1 xcexcm, the present invention can also be applied to ceramic powders having an average particle diameter beyond the range of about 0.01 to 1 xcexcm.
In a further aspect of the present invention, a method of producing ceramic slurry comprises passing mixed slurry containing a ceramic powder having an average particle diameter of about 0.01 to 1 xcexcm and a dispersion solvent through a predetermined passage under high pressure at a wall shear rate of about 106 (1/s) or more to disperse the ceramic powder in the mixed slurry.
The wall shear rate in the passage of the mixed slurry through the predetermined passage is set to about 106 (1/s) or more so that the ceramic powder can securely efficiently be dispersed with less damage to the ceramic powder during the passage of the mixed slurry through the predetermined passage.
The maximum shear stress and the wall shear rate have the following relation:
Maximum shear stress=Wall shear ratexc3x97Viscosity of slurry
In the method of producing ceramic slurry, the mixed slurry is passed through the passage under a pressure of about 100 kg/cm2 or more.
By applying a pressure of about 100 kg/cm2 or more, preferably about 300 kg/cm2 or more, to the mixed slurry, the wall shear rate in the predetermined passage can be set to about 106 (1/s) or more, or the maximum shear stress can be set to about 1000 (Pa) or more, thereby making the present invention effective.
In the method of producing ceramic slurry, the ratio (length/characteristic diameter) RL/D of length to characteristic diameter of the passage lies in the following range:
30xe2x89xa6RL/Dxe2x89xa61000
The characteristic diameter represents the following according to the sectional shape perpendicular to the axial direction:
(a) the short side of a rectangular sectional shape;
(b) the diameter of a circular shape;
(c) the short diameter of an elliptical shape; and
(d) the average depth of a fluid (=4xc3x97passage sectional area/total wetted length) in other sectional shapes.
The ratio (length/characteristic diameter) RL/D of length to characteristic diameter of the passage is set in the range of 30xe2x89xa6RL/Dxe2x89xa61000 so that the ceramic powder in the mixed slurry can be dispersed during the passage under practical conditions, thereby making the present invention more effective.
The reason for setting the ratio in the above range is that with RL/D of less than about 30, the ratio of the entrance region for the ceramic particles is increased to fail to obtain the sufficient disintegrating effect, while with RL/D of over about 1000, a pressure loss becomes excessive for the disintegrating effect.
In the method of producing ceramic slurry of the present invention, the passage has a substantially linear portion having a predetermined length in which a bent portion having a bending angle of 100xc2x0 or less, or a curved portion having a curvature radius of 3 mm or less is not formed on the upstream side and downstream side.
The substantially linear portion provided in the passage enables the ceramic powder to be securely dispersed by applying the maximum shear stress (about 1000 Pa or more) necessary for dispersing the ceramic powder. Since the substantially linear portion has neither a bent portion having a bending angle of 100xc2x0 or less nor a curved portion having a curvature radius of 3 mm or less on the upstream side and downstream side thereof, the ceramic powder can be prevented from being greatly damaged by collision or impact force before and after the supply of slurry to the passage, thereby making the present invention more effective.
A method of producing a green sheet of the present invention comprises forming ceramic slurry produced by the method of the present invention in a sheet on a predetermined substrate to form a ceramic green sheet having a thickness of about 0.1 to 10 xcexcm.
Since the ceramic slurry produced by the above-described method comprises the ceramic powder having an average particle diameter of about 0.01 to 1 xcexcm and sufficiently dispersed in the dispersion solvent, a high-quality ceramic green sheet having a small thickness (about 0.1 to 10 xcexcm) can securely be produced by forming the ceramic slurry in a sheet. It is possible to obtain a ceramic green sheet having excellent surface smoothness, a high density, high tensile strength, and uniformity in the distribution of resins such as the binder, the plasticizer, etc., and suitable for manufacturing a multilayer ceramic electronic part.
A method of producing a multilayer ceramic electronic part of the present invention comprises forming ceramic green sheets by using ceramic slurry produced by the method of the present invention, laminating a plurality of the ceramic green sheets together with base metal internal electrodes, cutting and burning the laminated product, and then forming external electrodes.
A plurality of the ceramic green sheets formed by using the ceramic slurry produced by the method of the present invention are laminated together with base metal internal electrodes, the laminated product is cut and burned, and the external electrodes are formed thereon to obtain a high-quality multilayer ceramic electronic part having desired properties and high reliability.
In a further aspect of the present invention, a method of producing ceramic slurry used for manufacturing a ceramic electronic part comprises the mixing disintegration step by an impact force-type high-pressure dispersion method in which a mixture of a ceramic powder having an average particle diameter of about 0.01 to 1 xcexcm and a dispersion solvent is ejected under a pressure of about 100 kg/cm2 to cause the mixture to collide with a solid wall made of a hard material at a velocity of about 100 m/s or more so that the ceramic powder is disintegrated to a desired state and dispersed to obtain mixed and disintegrated slurry, and the dispersion step by a shear stress-type high-pressure dispersion method in which the mixed and disintegrated slurry is passed through a predetermined passage under a high pressure of about 100 kg/cm2 or more at a flow rate which can apply a maximum shear stress of about 1000 Pa or more or a wall shear rate of about 106 (1/s) or more to the ceramic powder.
In a further aspect of the present invention, a method of producing ceramic slurry used for manufacturing a ceramic electronic part comprises the mixing disintegration step by an impact force-type high-pressure dispersion method in which a mixture of a ceramic powder having an average particle diameter of about 0.01 to 1 xcexcm and a dispersion solvent is ejected under a pressure of about 100 kg/cm2 from a plurality of opposite nozzles to cause the ceramic powder and the dispersion solvent to collide with each other at a velocity of about 50 m/s or more so that the ceramic powder is disintegrated to a desired state and dispersed to obtain mixed and disintegrated slurry, and the dispersion step by a shear stress-type high-pressure dispersion method in which the mixed and disintegrated slurry is passed through a predetermined passage under a high pressure of about 100 kg/cm2 or more at a flow rate which can apply a maximum shear stress of about 1000 Pa or more or a wall shear rate of about 106 (1/s) or more to the ceramic powder.
In the method of producing ceramic slurry of the present invention, the mixed and disintegrated slurry is obtained by the impact force-type high-pressure dispersion method in which the mixture of the ceramic powder having an average particle diameter of about 0.01 to 1 xcexcm and the dispersion solvent is ejected from a small nozzle or orifice to cause the mixture to collide with the solid wall or the materials ejected from nozzles are caused to collide with each other. Then, the mixed and disintegrated slurry is dispersed by the shear stress-type high-pressure dispersion method comprising passing the slurry through the small passage at a high velocity, thereby obtaining disperse slurry in which the ceramic powder is sufficiently dispersed.
Namely, the ceramic powder is dispersed by a combination of the impact force-type high-pressure dispersion method and the shear stress-type high-pressure dispersion method to uniformly disperse the ceramic powder while suppressing deterioration in crystallinity of the ceramic powder and an excessive increase in the specific surface area, thereby obtaining high-quality ceramic slurry.
In the present invention, the dispersion solvent may contain the dispersant, the plasticizer, and the antistatic agent, and further contain other additives.
In the present invention, in mixing and disintegration by the impact force-type high-pressure dispersion method, various means (mechanisms) such as a small nozzle, an orifice having a nozzle having a predetermined diameter and the like, can be used as means for ejecting the mixture of the ceramic powder and the dispersion solvent under pressure.
In the present invention, mixing and disintegration may be performed by the impact force-type high-pressure dispersion method with the binder added to the mixture.
Even in the mixing disintegration step performed with the binder added to the mixture, the ceramic powder can uniformly be dispersed without excessive damage to the ceramic powder, thereby producing high-quality ceramic slurry.
The time of addition of the binder is not limited, and the binder may be previously mixed with the dispersion solvent or mixed therewith at the time the ceramic powder is dispersed in the dispersion solvent.
In a further aspect of the present invention, a method of producing ceramic slurry used for manufacturing a ceramic electronic part comprises the mixing disintegration step of mixing a ceramic powder having an average particle diameter of about 0.01 to 1 xcexcm and a dispersion solvent containing no binder, and disintegrating the ceramic powder by the impact force-type high-pressure dispersion method to obtain mixed and disintegrated slurry, and the dispersion step of adding the binder to the mixed and disintegrated slurry and dispersing the resultant mixture by the shear stress-type high-pressure dispersion method.
The ceramic powder is mixed with the dispersion solvent containing no binder and disintegrated by the impact force-type high-pressure dispersion method to obtain the mixed and disintegrated slurry, and the binder is added to the mixed and disintegrated slurry, followed by dispersion by the shear stress-type high-pressure dispersion method to obtain disperse slurry in which the ceramic powder is further sufficiently dispersed.
Namely, the binder is partially gelled in the dispersion solvent in some cases, and thus the ceramic powder is mixed with the dispersion solvent and disintegrated by the impact force-type high-pressure dispersion method before the binder is added to improve the efficiency of mixing and disintegration, as compared with mixing and disintegration of the ceramic powder in a partially gelled state by the impact force-type high-pressure dispersion method. Therefore, the final dispersibility of the ceramic powder can be further improved.
In a further aspect of the present invention, a method of producing ceramic slurry used for manufacturing a ceramic electronic part comprises the mixing disintegration step of mixing a ceramic powder having an average particle diameter of about 0.01 to 1 xcexcm and a dispersion solvent containing no binder and disintegrating the ceramic powder by the impact force-type high-pressure dispersion method to obtain mixed and disintegrated slurry, the primary dispersion step of dispersing the mixed and disintegrated slurry by the shear stress-type high-pressure dispersion method to obtain primary disperse slurry, and the secondary dispersion step of adding the binder to the primary disperse slurry and dispersing the resultant mixture by the shear stress-type high-pressure dispersion method to obtain secondary disperse slurry (final disperse slurry).
The ceramic powder is mixed with the dispersion solvent containing no binder and disintegrated by the impact force-type high-pressure dispersion method to obtain the mixed and disintegrated slurry, and the mixed and disintegrated slurry is dispersed by the shear stress-type high-pressure dispersion method to obtain the primary disperse slurry. Then, the binder is added to the primary disperse slurry, and the resultant mixture is further dispersed by the shear stress-type high-pressure dispersion method. In this method, the ceramic powder can be uniformly dispersed without excessive damage to the ceramic powder to produce high-quality ceramic slurry.
In a further aspect of the present invention, a method of producing ceramic slurry used for manufacturing a ceramic electronic part comprises the primary mixing disintegration step of mixing a ceramic powder having an average particle diameter of about 0.01 to 1 xcexcm and a dispersion solvent containing no binder and disintegrating the ceramic powder by the impact force-type high-pressure dispersion method to obtain primary mixed and disintegrated slurry, the secondary mixing disintegration step of adding the binder to the primary mixed and disintegrated slurry and mixing and disintegrating the resultant mixture by the impact force-type high-pressure dispersion method to obtain secondary mixed and disintegrated slurry, and the dispersion step of dispersing the secondary mixed and disintegrated slurry by the shear stress-type high-pressure dispersion method to obtain disperse slurry.
The ceramic powder is mixed with the dispersion solvent containing no binder and disintegrated by the impact force-type high-pressure dispersion method to obtain the primary mixed and disintegrated slurry, and the binder is added the primary mixed and disintegrated slurry, followed by further mixing and disintegration by the impact force-type high-pressure dispersion method to obtain the secondary mixed and disintegrated slurry. Then, the secondary mixed and disintegrated slurry is dispersed by the shear stress-type high-pressure dispersion method. In this method, the ceramic powder can be uniformly dispersed without excessive damage to the ceramic powder to produce high-quality ceramic slurry.
The method of producing ceramic slurry of the present invention uses, as the binder, a binder solution obtained by mixing and stirring the solvent and the binder, and then dispersing the mixture by the shear stress-type high-pressure dispersion method comprising passing the mixture through a predetermined passage under a high pressure of about 100 kg/cm2 or more at a flow rate which can apply a maximum shear stress of about 1000 Pa or more or a wall shear rate of about 106 (1/s) or more.
By using the binder solution obtained by mixing and stirring the solvent and the binder, and then dispersing the mixture by the shear stress-type high-pressure dispersion method as the binder, the occurrence of gel, which is caused in direct addition of the binder, can be prevented to further improve the dispersibility of the ceramic powder.
The method of producing ceramic slurry of the present invention uses, as the binder, a binder solution obtained by mixing and stirring the solvent and the binder to form a binder mixed solution, and then heating the binder mixed solution under reflux at 40 to 100xc2x0 C. By using the binder solution obtained by mixing and stirring the solvent and the binder to form the binder mixed solution, and then heating the binder mixed solution under reflux at 40 to 100xc2x0 C. as the binder, the binder can be added in a state in which the binder is securely dissolved (a state without aggregation of xcexcm size), thereby further improving the dispersibility of the ceramic powder.
In the method of producing ceramic slurry of the present invention, the disperse slurry (final disperse slurry) has a viscosity of about 0.003 to 0.1 Pas. With the disperse slurry (final disperse slurry) having a viscosity of about 0.003 to 0.1 Pas, the ceramic slurry is suitable for use in the process for forming a ceramic green sheet, thereby making the present invention more effective.
A method of producing a green sheet of the present invention comprises forming ceramic slurry produced by the method of the present invention in a sheet on a predetermined substrate to form a ceramic green sheet having a thickness of about 0.1 to 10 xcexcm.
Since the ceramic slurry produced by the above-described method comprises the ceramic powder having an average particle diameter of about 0.01 to 1 xcexcm and sufficiently dispersed in the dispersion solvent, a high-quality ceramic green sheet having a small thickness (about 0.1 to 10 xcexcm) can securely be produced by forming the ceramic slurry into a sheet. Namely, it is possible to obtain a ceramic green sheet having excellent surface smoothness, a high density, high tensile strength, and uniformity in the distribution of resins such as the binder, the plasticizer, etc., and suitable for manufacturing a multilayer ceramic electronic part.
A method of producing a multilayer ceramic electronic part of the present invention comprises forming ceramic green sheets by using ceramic slurry produced by the method of the present invention, laminating a plurality of the ceramic green sheets together with base metal internal electrodes, cutting and burning the laminated product, and then forming external electrodes.
A plurality of the ceramic green sheets formed by using the ceramic slurry produced by the method of the present invention are laminated together with base metal internal electrodes, the laminated product is cut and burned, and the external electrodes are formed thereon to obtain a high-quality multilayer ceramic electronic part having desired properties and high reliability.
In a further aspect of the present invention, a method of producing a ceramic slurry composition containing a ceramic powder, a dispersant, a binder, and a solvent comprises mixing, at a predetermined ratio, at least (a) a ceramic powder, (b) a dispersant, and (c) a binder solution obtained by mixing a binder and a solvent to form a solution and dispersing the binder in the solution under a high pressure of about 100 kg/cm2 or more, and then dispersing the resultant mixture.
The solvent and the binder are previously mixed to form a solution, and the binder is dispersed in the under a high pressure of about 100 kg/cm2 or more to efficiently dissolve the binder in the solvent. The thus-obtained binder solution is mixed with the ceramic powder, and the dispersant at the predetermined ratio, and the mixture is dispersed to efficiently produce a ceramic slurry composition containing less undissolved binder. By using the ceramic slurry composition of the present invention, the ceramic green sheet having less defects can be efficiently produced.
The method of producing a ceramic slurry composition of the present invention uses as the binder a binder solution prepared by mixing the solvent and the binder to form a solution, dispersing the binder in the solution under a high pressure of about 100 kg/cm2 or more, and then filtering the solution. Since the viscosity of the binder is decreased by high-pressure dispersion, filtration with a filter having a small pore size can easily be carried out, thereby effectively removing the undissolved material. It is thus possible to securely produce ceramic slurry from which the undissolved material is precisely removed, thereby making the present invention more effective.
In a further aspect of the present invention, a ceramic slurry composition comprises at least a ceramic powder, a dispersant, a binder, and a solvent wherein a binder solution obtained by mixing a binder and a solvent to form a solution and dispersing the binder in the solution under a high pressure of about 100 kg/cm2 or more is used as the binder.
The solvent and the binder are previously mixed to form a solution, and the binder is dispersed in the solution under a high pressure of about 100 kg/cm2 or more to form the binder solution having excellent solubility of the binder, thereby obtaining ceramic slurry containing less undissolved binder. By using the ceramic slurry composition of the present invention, a ceramic green sheet having less defects can be efficiently produced.
In the present invention, the binder used may contain a plasticizer, and an antistatic agent, and further contain other additives.
In the present invention, the method of dispersing the ceramic powder, the dispersant, and the binder is not limited, and various dispersion methods such as a method using a medium-type dispersing machine such as a bead mill, a ball mill, an attritor, a pan shaker, a sand mill, or the like, a kneading method, a three-roll method, a high-pressure dispersion method, etc. can be used.
In the stage of the ceramic powder or the mixture of the ceramic powder and the dispersion solvent, the ceramic powder may be previously dispersed by using any one of the above various methods.
In preparing the ceramic slurry composition, the order of addition of the dispersant, the binder, etc. is not limited, but a preferred method comprises mixing the ceramic powder, the dispersant, and the solvent, adsorbing the dispersant on the ceramic powder by dispersion, and then adding the binder to the mixture, followed by further mixing and dispersion.
The ceramic slurry composition contains as the binder a binder solution prepared by mixing the solvent and the binder to form a solution, dispersing the binder in the solvent under a high pressure of about 100 kg/cm2 or more, and then filtering the solution.
Since the viscosity is decreased by dispersing the binder under high pressure to facilitate filtration with a filter having a small pore size, and thus the undissolved material can efficiently be removed to obtain ceramic slurry from which the undissolved material is precisely removed.
The ceramic slurry composition of the present invention comprises the ceramic powder having an average particle diameter of about 0.01 to 1 xcexcm.
The present invention is particularly useful for application to a ceramic slurry composition comprising a fine ceramic powder having an average particle diameter of about 0.01 to 1 xcexcm and used for producing a thin ceramic green sheet. By using the ceramic slurry composition comprising the ceramic powder having an average particle diameter of about 0.01 to 1 xcexcm and the binder solution used as the binder and subjected to the above-described high-pressure dispersion treatment, a thin ceramic green sheet having less defects can be efficiently produced. However, the present invention can also be applied to cases in which the average particle diameter is beyond the range of about 0.01 to 1 xcexcm.
A method of producing a ceramic green sheet of the present invention comprises forming the ceramic slurry composition of the present invention in a sheet on a predetermined substrate.
Since the ceramic slurry composition of the present invention contains less dissolved binder or substantially no dissolved binder, the ceramic slurry composition can be formed in a sheet to securely produce a high-quality thin ceramic green sheet having no defect. In producing a multilayer ceramic electronic part by using the ceramic green sheet, a high-quality multilayer ceramic electronic part having high reliability and desired properties can be obtained.
In the method of producing a ceramic green sheet of the present invention, the ceramic green sheet has a thickness of about 0.1 to 10 xcexcm.
Even with a small thickness (thickness=about 0.1 to 10 xcexcm), the method of the present invention can securely produce a high-quality ceramic green sheet suitable for use for manufacturing a multilayer ceramic electronic part.
A method of manufacturing a multilayer ceramic electronic part of the present invention comprises laminating a plurality of ceramic green sheets produced by the method of the present invention, cutting and burning the laminated product, and then forming external electrodes thereon.
The method comprising laminating a plurality of the ceramic green sheets produced by the method of the present invention, cutting and burning the laminated product, and then forming the external electrodes thereon can efficiently produce a multilayer ceramic electronic part having a low rate of short circuit and high reliability because of the use of the ceramic green sheets having less defects.